1. Field of the Invention
The present invention relates to a resin composition having good gas barrier properties against oxygen, carbon dioxide gas or the like, good moisture-resistance, good aroma retentivity, and good flavor barrier properties, and having an oxygen scavenging function. The present invention also relates to a multilayered container using such a resin composition that has a good appearance, in particular, good transparency, and significantly improved impact delamination resistance.
2. Description of the Related Art
Ethylene-vinyl alcohol copolymer (hereinafter may be abbreviated as EVOH) can be melt-molded, and has excellent gas barrier properties against oxygen or carbon dioxide gas. For this reason, a multilayered structure including a layer made of EVOH and a layer made of a thermoplastic resin having excellent moisture-resistance, mechanical properties or the like (e.g., thermoplastic polyester; hereinafter thermoplastic polyester may be abbreviated as PES) is utilized as various molded products that require gas barrier properties. For example, such a multilayered structure is used in various fields as a multilayered container, in particular, in the form of a bottle. For example, it is widely used in such fields as foods, drinks, medicines, cosmetics, toiletries or the like.
The multilayered container has good barrier properties against oxygen, carbon dioxide gas, and the like. However, the permeability thereof against gas such as oxygen is not exactly zero, unlike metals used for cans, etc. and glass used for bottles, etc. but still permits transmission of gas in an amount that cannot be neglected. In particular, for containers of foods, the degradation of food contents due to oxidation when they are preserved for a long time is of great concern. Therefore, improvement on the oxygen barrier properties is strongly desired.
On the other hand, when filling contents in the container, oxygen may be mixed in the container together with the contents. When the contents are susceptible to oxidization, only a trace amount of oxygen may degrade the quality of the contents. In order to prevent this, providing a material of the container with an oxygen scavenging function has been proposed. In this case, oxygen that might enter from the outside of the container to the inside can be scavenged, so that the gas barrier properties of a packaging material also can be improved.
For example, as the method of providing the oxygen scavenging function to the EVOH that constitutes a packaging material, the following methods are known: (1) An oxidation catalyst such as a transition metal is added to the EVOH to make the EVOH susceptible to oxidation, thereby providing the oxygen scavenging function to the EVOH (Japanese Laid-Open Patent Publication (Tokkai) No.4-211444); (2) A resin composition substantially composed of polyolefin and an oxidation catalyst, that is, polyolefin in a state susceptible to oxidation, is dispersed in the EVOH, thereby providing the oxygen scavenging function to the EVOH (Japanese Laid-Open Patent Publication (Tokkai) No.5-156095); and (3) EVOH, polyolefin, and an oxidation catalyst are blended to make the EVOH and polyolefin susceptible to oxidation, thereby providing the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No.5-170980). However, method (1) fails to provide sufficiently improved oxygen barrier properties. Methods (2) and (3) have a drawback in that the transparency is impaired significantly.
Furthermore, in the multilayered containers, especially when an adhesive resin layer is not provided between the layers, delamination between the thermoplastic resin layer (e.g., PES layer) and the EVOH layer is likely to occur, which causes a large problem in the appearance. In order to solve this problem, a multilayered container made of a PES layer and an EVOH composition layer having a specific structure has been proposed (Japanese Laid-Open Patent Publication (Tokkai) No.11-348196). However, the oxygen barrier properties of such a multilayered container still does not exceed the level of a conventional EVOH, and further improvement is in demand.